Epistemic status: I've noticed most AI safety folks seem more optimistic about mechanistic interpretability than I am. This is just a quick list of reasons for my pessimism. Note that I don’t have much direct experience with mech interp, and this is more of a rough brain dump than a well-thought-out take.
For example, recently GDM decided to deprioritize SAEs. I think something like a year ago many people believed SAEs are "the solution" that will make mech interp easy? Pivots are normal and should be expected, but in short timelines we can't really afford many of them.
What we have: "This is a statement about horses, and you can see that this horse feature here is active"
What we need: "Here is how we know whether a statement is about horses or not"
Note that these things might be pretty far away, consider e.g. "we know this substance causes cancer" and "we can tell for an arbitrary substance whether it causes cancer or not".
Or maybe there are some and I don't know them?
Anyway, I feel people often say something like "If we find the deception feature, we'll know whether models are lying to us, therefore solving deceptive alignment". This makes sense, but how will we know whether we've really found the deception feature?
I think this is related to the previous point (about exists/all quantifiers): we don't really know how to build mech interp tools that give some guarantees, so it's hard to imagine what such solution would look like.
I think ASI probably won't be a simple non-recurrent transformer. No strong justification here - just the very rough "It's unlikely we found something close to the optimal architecture so early". This leads to two problems:
The fact that things like steering vectors or linear probes or SAEs-with-some-reasonable-width somewhat work is a nice feature of the current systems. There's no guarantee that this will hold for the future, more efficient, systems - they might become extremely polysemantic instead (see here). This is not necessarily true: maybe an optimal network learns to operate on something like natural abstractions, or maybe we'll favor interpretable architecture over slightly-more-efficient-but-uninterpretable architectures.
----
That's it. Critical comments are very welcome.
I lay out my thoughts on this in section 6.6 of the deepmind AGI safety approach. I broadly agree the guarantees seem pretty doomed. But I also think guarantees just seem obviously doomed by all methods because neural networks are far too complex and we'll need to have plans that do not depend on them. I think there are much more realistic use cases for interpretability than aiming for guarantees